Distribution of full motion video data has evolved from early television broadcasting to meet viewer demand. Earliest video distribution was by point-to-point wiring between a camera and a video monitor. This was followed by scheduled television broadcasting of programming over the public air waves. In the 1960s, Community Antenna Television (CATV) was chartered to provide off-air television signals to viewers in broadcast reception fringe areas. Later, under FCC regulation, the CATV industry was required to provide local access and original programming in addition to off-air broadcast signal distribution.
In response, several sources of cable network programming were established. Because of the wide bandwidth available on cable television systems, additional channels were made available for the new programming. However, programming was generally prescheduled, with the viewer left to tune to the designated channel at the appointed time to view a particular program.
To increase revenues, cable television systems have initiated distribution of premium channels viewable only by subscribers having appropriate descramblers. The descramblers are tuned to receive only premium channels, descramble the video and audio information and supply a signal capable of reception on a standard television set.
Pay-per-view programs, which evolved later, include recently released movies, live concerts and popular sporting events. Subscribers wishing to view a pay-per-view program place an order with the cable operator. At the designated time, the subscriber's descrambler is activated to permit viewing of the pay-per-view programming. However, the subscriber is restricted to viewing the programming at the scheduled time. There is no capability of delivering programming to a subscriber on demand, that is, immediately or at a subscriber-specified time and date.
In the early 1980s, technological advances resulted in the proliferation of Video Cassette Recorders (VCR), establishing a second course for video programming distribution. Pre-recorded video programs are now available for sale and rental to VCR owners. Using a VCR, the viewer selects from among many titles available for sale and rental, and views the program when convenient. The VCR owner further has the capability to selectively view the programming using special functions of the VCR, such as pause, fast forward, reverse, slow motion, etc. The viewer can thus manipulate and replay portions of the program at will.
The penalty for this convenience, however, is in the necessity to travel to the local video rental/sales store, if necessary wait for a popular video program tape to become available, once the program is obtained return home to view it and then revisit the video store to return the tape.
Telephone lines have been suggested as an alternative means of video distribution. However, systems using the public switched telephone network (PSTN) are often bandwidth limited, providing generally only still frame or video conferencing capabilities. Because telephone system carriers for the most part use the PSTN only for connectivity between subscribers, there is no capability for dynamic routing of digitized video without dedicated leased, wide bandwidth circuits. Telephone line based systems also fail to provide acceptable VCR type functional control of the programming.
U.S. Pat. No. 5,247,347 to Litteral et al., the disclosure of which is hereby incorporated in its entirety into this disclosure by reference and over which the present invention is an improvement, discloses an enhanced public switched telephone network which also provides a video on demand service to subscribers over the PSTN. A menu of video programming information is accessible at the subscriber's premises. The subscriber may transmit ordering information via the PSTN to the independent video information providers. Video programming may be accessed and transmitted to the subscriber directly from a video information provider (VIP) or through a video buffer located at a central office (CO) serving the subscriber.
The VIP transmits coded digital video data over wideband PSTN supplied connectivity to a central office. The video data may be buffered at the central office for transmission over a POTS line to the subscriber. A subscriber may use either a standard telephone instrument over the PSTN or a dedicated control device over an ISDN or X.25 packet network to order the video programming. Such a device is located at a television set of the subscriber and permits a display of the program menu on the television screen.
Connectivity between the central office and the subscriber for transmission of video data is provided by an asymmetrical digital subscriber line (ADSL) system. ADSL interface units perform multiplexing of digital video information with voice information to be transmitted to the subscriber and support transmission on the packet data network of one or more reverse control channels from the subscriber to the central office.
FIG. 1 depicts a prior art video on demand system, transmitting compressed, digitized video data of the type disclosed by the Litteral et al. Patent. The video on demand system shown in FIG. 1 utilizes the existing Public Switched Telephone Network (PSTN) and implements compression techniques for storing and transmitting video information. The switching facilities are located in central offices (COs) 100 serving residential customers or subscribers. Electronic devices such as ADSL interfaces 105 associated with the subscriber loops modify the transmission characteristics of the subscriber loops to permit delivery of full motion video information over existing telephone wiring (subscriber loop) plant facilities.
In the Litteral Patent, the ADSL interface units are located at the central office and at the subscriber's location. As disclosed in the Litteral Patent, the ADSL interface units combine video information together with bidirectional signalling and a plain old telephone service (POTS) for transmission over an ordinary telephone wiring plant.
Certain problems arise with the prior art type ADSL transmission systems. When environmental interference situations arise, ADSL transmission is more sensitive than POTS. As transmission distances over copper wire pairs exceed 18,000 feet, the ADSL of the prior art becomes marginal or infeasible. If the copper plant has loading coils, repeaters, or bridge taps, or experiences corrosion or moisture, ADSL operation may be infeasible. In the event the copper facilities available between the central office and the subscriber's premises are not continuous (e.g. at least a portion of the loop runs on a subscriber loop carrier system), ADSL operation will generally not be feasible.
The system of the present invention solves these problems and provides an number of other advantages over earlier ADSL systems.